Internal combustion engines including reciprocating pistons and rotating output shafts are well known in the art. These engines utilize a cycle including expansion, exhaust, intake and compression phases to convert the reciprocating motion of the engine pistons into rotational motion of the output shaft. Such engines conventionally use either four or two stroke cycles. In a four stroke cycle engine, the engine cycle is affected within four strokes of a working piston. In a two stroke cycle engine, all four phases of the cycle are affected within two strokes of a working piston.
Each of the two and four stroke engines have their own advantages and disadvantages. Two stroke engines include a relatively simple arrangement of ports for transferring an air fuel mixture charge and exhaust gases to and from the piston cylinder respectively. Advantageously, two stroke engines also develop power on each rotation of a crank shaft. This contrasts with four stroke engines which generate power only on every other rotation of the crank shaft. Accordingly, it should be appreciated that two stroke engines provide an improved power to weight ratio. Two stroke engines do, however, suffer from several disadvantages including poor scavenging characteristics and fuel efficiency. Two stroke engines also tend to generate combustion gases with a high pollution content.
In contrast, four stroke engines provide better scavenging and fuel efficiency. When in tune, four stroke engines also generate combustion gases with a relatively low pollution content when compared to two stroke counterparts. Four stroke engines do, however, also suffer from a number of disadvantages. For example, a four stroke engine includes a relatively complicated valve mechanism to regulate exhaust and intake charge flow. Additionally, as indicated above, four stroke engines only generate power on every other rotation of the crankshaft. Accordingly, they do not provide a desirable high power to weight ratio.
It has been found that the utilization of a cam and swashplate structure instead of a crankshaft permits greater flexibility in two and four stroke engine construction. For example, this structure makes it possible to arrange pistons in horizontally opposed construction. Such a construction exhibits a compactness not possible with crankshaft designs. Advantageously, such a construction also reduces the number of moving parts and provides greater power to weight ratio. Further, by adjusting the cam profile, port opening and closing positions may be set to obtain better scavenging in two stroke engine designs. Similarly, in four stroke engine designs, the utilization of an irregular cam plate profile makes it possible to provide expansion and intake strokes of significantly different lengths. Thus, the possibility of providing an engine with a greater expansion efficiency is attained.
One recent example of a horizontally opposed construction internal combustion engine is found in U.S. Pat. No. 4,565,165 to Papanicolaou. The Papanicolaou engine includes two cylinders. Each cylinder houses a pair of opposed piston assemblies. The cylinders include intake and exhaust ports in the cylinder walls that control the flow of air through the combustion chambers. As shown, the intake ports are connected to a supercharger that is attached to and driven by the output shaft of the engine.
While the engine disclosed in the Papanicolaou patent provides a high power to weight ratio with improved combustion efficiency and fuel economy, further improvements in engine designs particularly of the horizontally opposed construction are possible. More particularly, still better scavenging and air fuel charge flow are desirable. Similarly, so is a further improvement in fuel efficiency. Additionally, an engine of simpler construction that is both less expensive to produce and easier to manufacture and maintain is also desired.